Papers by Author: N. Darowski

Abstract: Solid state reactions between amorpous Si and crystalline Co have been investigated by synchrotron radiation at Bessy (Berlin, Germany). The multilayered samples (with 10 periods of a-Si(15 nm)/Co(15 nm) layers) were produced by magnetron sputtering and isothermally heat treated at temperatures between 523 and 593 K. From the time evolution of the XRD spectra first the growth rate of the CoSi phase as well as the decay rate of the Co layer we determined (at 523 and 543 K). The kinetics were described by a power law; tk, and for the growth of CoSi k=0.65 while for the loss of the Co the k=0.77 was obtained, respectively. At higher temperatures (at 573 and 593 K) the formation and growth of the Co2Si layer, at the expense of the Co and already existing CoSi layers, was observed with exponents of about 1 for all the above kinetics. These results, together with the results of resistance kinetics measurements, in similar multilayered as well as bi-layered samples at similar temperatures, providing similar exponents will be presented. Possibility of the interface reaction control and/or the effect of the diffusion asymmetry (which was recently published for the interpretation of solid state reactions with non-parabolic kinetics on the nanoscale) will be discussed.

Abstract: The profiles of 001 and 002 reflections have been measured at 1173 K as a function of time by means of X-ray diffraction (XRD) on tensile-creep deformed specimens of single crystal superalloy SC16. Decrease in line width (full width at half maximum: FWHM) by about 7 % and increase in peak position by about 3x10-4 degrees was detected after 8.5x104 s. Broadening of the 002 peak profile indicated a more negative value of the lattice misfit after the same time period. The results are discussed in the context of the anisotropic arrangement of dislocations at the γ/γ’ interfaces during creep and their rearrangement during the thermal treatment at 1173 K.

Abstract: Specimens of single crystal superalloy SC16 have been pre-deformed at 1223 K to strain of 15 % under tensile load of 150 MPa. The profiles of the 001 superlattice reflection of the γ’ precipitate phase as well as the profiles of the 002 reflections of the fcc matrix phase and of γ’-precipitate phase have been measured between RT and 1073 K by means of X-ray diffraction (XRD). From these measurements the lattice distortion of the γ’ precipitates and the lattice misfit between γ and γ’ phase have been determined as a function of temperature. The width of the 001 reflection as well as the lattice misfit decreased as a function of temperature. The results are ascribed to the anisotropic arrangement of dislocations at the γ/γ’ interfaces and to the different thermal expansion coefficients of the γ- and γ’-phase. A comparison of lattice misfit with previous measurements on moderately strained specimens suggests that the measured changes in lattice structure are predominantly created in stage I of creep-deformation.